No abstract

Double ionization of helium is investigated for 60-, 120-, and 420-MeV/u (v/c =0.34-0.72)U +-ion impact. The measured double-to-single ionization ratios indicate that, even for these very high velocities, double ionization of the He target results predominantly from independent interactions of the projectile with both target electrons. It is concluded that the asymptotic high-velocity regime for one-step double ionization (i.e. , "shakeoff") has not yet been reached even for U projectiles at 420 MeV/u, and, in fact, cannot be reached for projectiles with q 7, thereby verifying that the ionic charge is fully as important as the velocity in determining the importance of a given ionization mechanism.PACS number(s): 34.50.Fa

Total cross sections are presented for the production of various stages of multiple ionization of the target in coincidence with the final projectile charge state for collisions of F6+ with Ne at 10 and 15 MeV. In particular, the current measurements are compared with the results of a new classical trajectory Monte Carlo method in which electrons are included explicitly on both target and projectile ( ~C T M C ) and with those based on the conventional independent electron model ( I E M ) . It is shown by the good agreement with experiment that the n C T M C model simultaneously represents well the ionization, charge transfer and excitation channels for both target and projectile. Further, it is demonstrated that the I E M is in clear disagreement with the present experiment and is inadequate to predict the outcome of such multi-electronic transition processes. However, the IEM is shown to provide a reasonable estimate of the free electron production, that is, the cross section summed over charge states weighted by the number of electrons liberated. The I E M is also used to illustrate a process in cusp electron production where electrons are interchanged between the target and projectile.

Multiple ionisation cross sections u (q) for the production of recoil ions in charge state q by 120 MeV U-' U90+ impact have been measured for Ne, Ar and Kr targets using a recoil-ion-projectile-electron triple-coincidence technique. The data are compared with previously measured cross sections for U-ion impact in the projectile energy (E,) range from 1.4 to 420 MeV U-'. For low recoil-ion charge states a (q) decreases over the whole E , range somewhat more slowly than l/E,, whereas for higher recoil-ion charge states a (q) reaches a maximum at about 10-15 MeVu-'. The data are nicely described by parameter-free n-body Classical Trajectory Monte Carlo (~C T M C) calculations. The calculations indicate the importance of accounting for the Auger events in the description of the multiple ionisation process. Because of the smooth E , dependence of "(4) towards high E , , the development of a recoil-ion source using a primary U-ion beam in a storage ring for the production of high charge state recoil-ions appears to be feasible.